Introduction and Disclaimer

These worked examples illustrate the use of the BUGS language and sampler in a wide range of problems. They contain a number of useful ``tricks", but are certainly not exhaustive of the models that may be analysed.

We emphasise that all the results for these examples have been derived in the most naive way: in general a burn-in of 500 iterations and a single long run of 1000 iterations. This is not recommended as a general technique: no tests of convergence have been carried out, and traces of the estimates have not even been plotted. However, comparisons with published results have been made where possible. Times have been measured on a 60 MHz superSPARC: a 60 MHz Pentium PC appears to be about 4 times slower, and a 30 MHz superSPARC about 2 times slower.

Users are warned to be extremely careful about assuming convergence, especially when using complex models including errors in variables, crossed random effects and intrinsic priors in undirected models.

Warning
BUGS version 0.5
Release date: September 13, 1999

BUGS version 0.5 released on September 13, 1999 is a TEST version only.

If you encouter any errors in the program, please notify us by e-mailing bugs@mrc-bs.cam.ac.uk. In particular, users are warned that BUGS version 0.5 may crash during sampling with the error

Can not locate mode of sampling density

or

Allowed number of function evaluations exceeded for ARS.

Such errors typically occur when estimating models involving a log or logit function of parameters whose values are very close to zero. We are currently working to fix this bug, and will release a revised version 0.5 when this has been sorted out. Please note that the Cosmos example in BUGS Examples Volume 2 crashes with this error when running BUGS version 0.5, although the model can be run successfully using BUGS version 0.30.